Help me in solving Richardson extrapolation problem

Suppose N1(h) is a formula that produces O(h) approximations to a number M and that M=N1(h)+k1(h)+k2h^2...For a collection of positive constants k1, k2...Then N1(h), N1(h/2), N1(h/4) are all lower bounds for M. What can be said about the extrapolated approximations to N2(h), N3(h)...?